In the prior art, a second-generation mobile communications technology (2G, Second Generation)/third-generation mobile communications technology (3G, Third Generation) network supports both a circuit switched domain (CS domain, Circuit Switched Domain) and a packet switched domain (PS domain, Packet switched Domain), but a long term evolution (LTE, Long Term Evolution) network only provides a PS domain.
Currently, mainly a CS domain provides common voice services and short message services, and mainly a PS domain provides data services. The voice services are dominant services for mobile carriers currently. As the technologies of voice over mobile networks (VOIP, Voice over Internet Protocol) are not mature yet, a CS domain is still to bear voice services for a very long time in the future.
With the development of technologies, an LIE technology began to be used. The absence of a CS domain in an LTE system makes it difficult to effectively support voice services and short message services. Meanwhile, the 2G/3G network has undergone long-term construction and has good network coverage, and it is impossible to abandon this network in a short term. Therefore, in the future a carrier requires a user equipment (UE, User Equipment) to be capable of being attached to both a 2G/3G network and an LTE network, and a single card dual standby UE is such a UE. The single card dual standby UE adopts two antennas and two radio frequency modules, so that the single card dual standby UE is capable of being attached to both a 2G/3G network and an LTE network. In addition, to prevent increase of location update signaling caused by frequent movement of the UE between different systems, a network side may support an idle mode signaling reduction (ISR, Idle Mode Signalling Reduction) mechanism.
A basic concept of a signaling reduction solution is as follows: For a 2G/3G and an LTE/system architecture evolution (SAE, System Architecture Evolution) adjacent to each other, a routing area of the 2G/3G and a tracking area of the LTE/SAE are set as equivalent location areas. When a UE enters an access system, registration is performed according to a common registration/update procedure. The network allocates a temporary identifier and a location area identifier for the UE. When the network side supports the ISR mechanism, a location area update process is initiated if the UE enters another access system, and the network allocates the temporary identifier and the location area identifier of the new system. At this time, core network nodes that provide services for the UE in the two systems register with a home subscriber server (HSS, Home Subscriber Server), and at the same time provide services for the UE. However, when the UE moves between the two systems again, with the presence of an association relationship, the registration/update process no longer needs to be initiated, so that the objective of reducing route update signaling is achieved.
However, when the UE currently does not have a data service or data traffic is low, the UE also needs to be attached to both the 2G/3G network and the LTE network. Two radio frequencies are turned on, power consumption is large, and user experience is degraded.